Chad Hammerschmidt | Wright State University (original) (raw)
Papers by Chad Hammerschmidt
Goldschmidt2021 abstracts
Environmental Toxicology and Chemistry
The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data prod... more The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. Th...
Environmental science & technology, Jan 17, 2018
Historical reconstruction of mercury (Hg) accumulation in natural archives, especially lake sedim... more Historical reconstruction of mercury (Hg) accumulation in natural archives, especially lake sediments, has been essential to understanding human perturbation of the global Hg cycle. Here we present a high-resolution chronology of Hg accumulation between 1727 and 1996 in a varved sediment core from the Pettaquamscutt River Estuary (PRE), Rhode Island. Mercury accumulation is examined relative to (1) historic deposition of polycyclic aromatic hydrocarbons (PAHs) and lead (Pb) and its isotopes (Pb/Pb) in the same core, and (2) other reconstructions of Hg deposition in urban and remote settings. Mercury deposition in PRE parallels the temporal patterns of PAHs, and both track industrialization and regional coal use between 1850 and 1950 as well as rising petroleum use after 1950. There is little indication of increased Hg deposition from late 19th-century silver and gold mining in the western U.S. A broad maximum of Hg deposition during 1930-1980, and not found in remote sites, is consi...
Deep Sea Research Part I: Oceanographic Research Papers, 2016
Low-molecular weight thiols, including cysteine and glutathione, are biomolecules involved in a v... more Low-molecular weight thiols, including cysteine and glutathione, are biomolecules involved in a variety of metabolic pathways and act as important antioxidant and metal buffering agents. In this last capacity, they represent a potential mechanism for modulating the bioavailability and biogeochemistry of many trace elements in the ocean, particularly for chalcophilic elements (e.g., Cu, Zn, Cd, Ag and Hg). For this reason, and in the context of the international GEOTRACES program that seeks to understand the biogeochemistry of trace elements in the ocean, we measured the concentration of individual dissolved low-molecular weight thiols during the U.S. GEOTRACES North Atlantic Zonal Transect (USGNAZT). Only two thiols were identified, cysteine and glutathione, in contrast to results from the northeast subarctic Pacific Ocean, where the dipeptides glycine-cysteine and arginine-cysteine were also present and -glutamylcysteine was dominant. Concentrations of cysteine and glutathione in the North Atlantic Ocean were lower than in the Pacific and ranged from below detection (~0.01 nM) to 0.61 nM of cysteine and up to 1.0 nM of glutathione, with cysteine generally more abundant than glutathione. Vertical profiles of cysteine and glutathione were broadly consistent with their biological production, being more abundant in surface water and usually below detection at
Environmental science & technology, Jan 18, 2016
Metals in sediment can be complexed by minerals, partition between solid and aqueous phases, and ... more Metals in sediment can be complexed by minerals, partition between solid and aqueous phases, and cause toxicity at high concentrations. We studied how the oxidation of surface sediment that occurs during aging alters the partitioning and toxicity of Ni. Two sediments (Burntwood and Raisin) were amended with Ni, equilibrated, incubated in a flow-through flume, and examined for sediment physicochemistry and toxicity to Hyalella azteca (7 day growth). Through time, the sediment surface (5 mm) was oxidized, acid-volatile sulfide concentrations declined in Raisin sediment, and amorphous Fe oxides increased. Porewater Ni concentrations declined through time but total Ni concentrations in sediment were unchanged, suggesting changes in Ni partitioning through time. Both sediments elicited a toxic dose-response by H. azteca early in the aging process; but only Burntwood, for which Ni was primarily partitioned to Fe oxide minerals, exhibited a consistent dose-response during aging. Low total ...
ABSTRACT Abstract (2 leaves) bound with copy. Thesis (Ph. D.)--University of Connecticut, 2005. I... more ABSTRACT Abstract (2 leaves) bound with copy. Thesis (Ph. D.)--University of Connecticut, 2005. Includes bibliographical references. Adviser: William F.
Environmental Science Technology, 2005
Development of the early life stages of fishes can be affected adversely by methylmercury (MeHg) ... more Development of the early life stages of fishes can be affected adversely by methylmercury (MeHg) transferred from the maternal parent to the developing egg. We examined maternal transfer of MeHg to eggs of fathead minnows Pimephales promelas and evaluated the role of maternal MeHg burden versus that in the maternal diet during oogenesis on egg concentrations. Juvenile fish were fed one of four diets until sexual maturity (phase 1): A control diet (0.06 µg of Hg g-1 dry weight) and three that were contaminated with MeHg at 0.88 (low), 4.11 (medium), and 8.46 µg of Hg g-1 (high). At sexual maturity, female fish were paired with a male, again fed one of the four diets, and allowed to reproduce (phase 2). To assess the significance of female dietary exposure during oogenesis on MeHg in eggs, some fish were fed diets during phase 2 that differed from those during phase 1. Mean concentrations and burdens of MeHg in eggs from fish fed the same diet throughout the experiment varied with MeHg content of the maternal diet and were related positively to levels in the carcass of the maternal fish. However, MeHg in eggs was not proportional to that in carcasses among dietary treatments; MeHg in eggs from adults fed the control, low, medium, and high MeHg diets averaged 14%, 25%, 32%, and 35% of that in adults. For fish fed the control diet as juveniles and MeHg-contaminated diets after reaching sexual maturity, MeHg in eggs increased rapidly with duration of maternal dietary exposure prior to spawning. Moreover, concentrations of MeHg in eggs from fish fed the same contaminated diet as both juveniles and sexually mature adults were not related to the duration of adult exposure, and they were not appreciably greater than those from fish fed contaminated diets only just prior to spawning. These results indicate that the diet of the maternal adult during oogenesis, and not adult body burden, is the principal source of MeHg in fish eggs. Accordingly, the exposure of embryonic wild fishes to MeHg depends on levels of the contaminant in prey of the adult during oogenesis, which can vary intra-and interannually.
Environ Sci Technol, 1999
We examined the influence of maternal mercury and selected lacustrine variables on the mercury co... more We examined the influence of maternal mercury and selected lacustrine variables on the mercury content of eggs from yellow perch (Perca flavescens). Total mercury, methylmercury, and inorganic mercury were determined in eggs and carcasses (less eggs) from three seepage lakes with a pH range of 6.1-7.0 and a fourth lake in which pH was experimentally increased from 5.5 to 6.8 by addition of alkaline groundwater. The concentration of total mercury in eggs was strongly correlated with that in the maternal carcass. Concentrations and burdens of mercury in eggs and carcasses were inversely correlated with lake water pH, acid-neutralizing capacity, calcium, and dissolved organic carbon. In eggs containing more than 30 ng/g dry weight (4.5 ng/g wet weight) of total mercury, methylmercury averaged 91% of total mercury and ranged from 85% to 96%. Mean burdens of total mercury in individual eggs varied greatly among lakes (range, 2.3-63 pg), and the egg mass averaged 1.9% of the whole-body burden. We conclude that exposure of the developing yellow perch embryo to methylmercury is strongly affected by maternal bioaccumulation, which can vary substantially among and within lakes; however, the toxicological significance of the observed exposure of embryos to methylmercury is unclear.
Environmental Science and Technology, Sep 1, 2003
A new method for the determination of the concentration and conditional stability constant of dis... more A new method for the determination of the concentration and conditional stability constant of dissolved organic matter that binds mercury (Hg) has been developed using an in vitro assay of reducible Hg. The technique is a wet chemical analogue to electrochemical approaches now in use for ligand studies of many other trace transition metals in natural waters. Ligand characteristics are obtained from additions of ionic Hg to buffered lake, river water, and seawater and determination of the wet chemically reducible fraction following equilibration of the spike. This approach is robust, as demonstrated by (i) analysis using three reducing agents of varying strengths, (ii) replicate analyses, (iii) comparison to well-characterized complexing species (chloride and EDTA) using a competitive ion-exchange resin, and (iv) kinetic studies. Results indicate that Hg-complexing equivalents are present in the dissolved phase (<0.2 microm) ranging from <1 to >60 nN concentrations and with log conditional stability constants (log K') in the range of 21-24. Only one ligand class was found in the natural waters analyzed. There was indirect evidence for a class of organic ligands that formed reducible complexes with Hg in freshwater. Such ligand characteristics indicate that the vast majority of ionic inorganic Hg dissolved in freshwater and coastal saltwaters is associated with organic complexes. Concentrations, affinities, and kinetics implicate multidentate chelation sites as the principal complexing moieties for Hg and discourage the use of humic carboxylic acids as a proxy for the ligands/functional groups.
Environmental Science & Technology, 2016
Environmental Toxicology and Chemistry, 2015
Periphyton uptake of bioaccumulative methylmercury (MeHg) may be an important entryway into the f... more Periphyton uptake of bioaccumulative methylmercury (MeHg) may be an important entryway into the food web of many stream ecosystems where periphyton can be dominant primary producers. The net production of MeHg in stream sediment, its bioaccumulation in periphyton, and potential toxicity of divalent Hg (Hg(II)) and MeHg in sediment to periphyton were investigated with a 67-day in situ incubation experiment using chemical exposure substrates containing either a fine-grained, organic-rich or sandy, low-organic sediment, each amended with varying concentrations of mercuric chloride. MeHg was produced in sediment and concentrations increased with greater amounts of added Hg(II); however, the net production of MeHg was inhibited in the highest Hg(II) treatments of both sediments. The range of total Hg concentrations that inhibited MeHg production were between about 80,000 and 350,000 ng Hg per gram of organic matter for both sediments. Periphyton colonizing substrates accumulated MeHg in proportion to the concentration in sediment, but periphyton exposed to the sandy sediment accumulated about 20-fold more than those exposed to the organic-rich sediment relative to sediment MeHg concentrations. Toxicity of either Hg(II) or MeHg to periphyton was not observed with either periphyton organic content, net primary production, or respiration as endpoints. These results suggest that in situ production and bioaccumulation of MeHg in stream ecosystems can vary as a function of sediment characteristics and Hg(II) loadings to the sediment. This article is protected by copyright. All rights reserved.
Environmental Pollution, 2015
Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended so... more Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended solids (TSS), and other complexing ligands; however, no studies have examined the relative importance of Ni exposure through different compartments (water, sediment, food). Hyalella azteca and Lymnaea stagnalis were exposed to Ni-amended water, sediment, and food, either separately or in combination. Both organisms experienced survival and growth effects in several Ni compartment tests. The DOC amendments attenuated L. stagnalis Ni effects (survival, growth, and (62)Ni bioaccumulation), and presence of TSS exposures demonstrated both protective and synergistic effects on H. azteca and L. stagnalis. (62)Ni trophic transfer from food to H. azteca and L. stagnalis was negligible; however, bioaccumulating (62)Ni was attributed to (62)Ni-water ((62)Ni flux from food), (62)Ni-TSS, and (62)Ni-food. Overall, H. azteca and L. stagnalis Ni compartment toxicity increased in the following order: Ni-water > Ni-sediment > Ni-all (water, sediment, food) > Ni-food.
Environmental Science & Technology, 2015
To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico... more To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico (GOM) fish, we quantified fluxes of total Hg and MeHg from 11 rivers in the southeastern United States, including the 10 largest rivers discharging to the GOM. Filtered water and suspended particles were collected across estuarine salinity gradients in Spring and Fall 2012 to estimate fluxes from rivers to estuaries and from estuaries to coastal waters. Fluxes of total Hg and MeHg from rivers to estuaries varied as much as 100-fold among rivers. The Mississippi River accounted for 59% of the total Hg flux and 49% of the fluvial MeHg flux into GOM estuaries. While some estuaries were sources of Hg, the combined estimated fluxes of total Hg (5200 mol y(-1)) and MeHg (120 mol y(-1)) from the estuaries to the GOM were less than those from rivers to estuaries, suggesting an overall estuarine sink. Fluxes of total Hg from the estuaries to coastal waters of the northern GOM are approximately an order of magnitude less than atmospheric deposition rates. However, fluxes from rivers are significant sources of MeHg to estuaries and coastal regions of the northern GOM.
Environmental toxicology and chemistry / SETAC, Jan 27, 2015
Sediments in navigation-dominated waterways are frequently contaminated with a variety of particl... more Sediments in navigation-dominated waterways are frequently contaminated with a variety of particle-associated pollutants and are subject to frequent short-term resuspension events. There is little information documenting whether resuspension of metal-contaminated sediments has adverse ecological effects on resident aquatic organisms. Using a novel laboratory approach, we examined the mobilization of Zn, Cu, Cd, Pb, Ni and Cr during resuspension of a freshwater and two coastal marine sediments and whether resuspension and redeposition resulted in toxicity to model organisms. Sediment flux exposure chambers (SeFEC) were used to resuspend metal-contaminated sediments from one site in Lake DePue, Illinois, and two sites in Portsmouth Naval Shipyard, Maine. Short-term (4 h) resuspension of sediment at environmentally relevant suspended particulate matter concentrations (< 1 g/L) resulted in metal mobilization to water that was sediment and metal specific. Overall, the net release of m...
Our research in the U.S. Arctic is focused on (a) atmospheric Hg deposition and contamination of ... more Our research in the U.S. Arctic is focused on (a) atmospheric Hg deposition and contamination of lakes and watersheds, (b) in-lake cycling of Hg, especially methylHg, and (c) the behavior and fate of elemental Hg, whose production and mobilization via water-air exchange are quite significant. These studies are being conducted in the lacustrine and tundra wetland environs near the Arctic LTER Site at the Toolik Field Station (68\deg 38' N, 149\deg 38' W). Atmospheric Hg deposition over the last several centuries has been established with dated sediment archives from five carefully selected (i.e., headwater; small watershed) remote arctic lakes. Mercury budgets for the study lakes have been constructed from atmospheric, water column, watershed, and sedimentary investigations. Results indicate that (1) impact from anthropogenic Hg in the Arctic is of similar magnitude to that at temperate latitudes; (2) whole-lake Hg sedimentation determined using 55 210Pb-dated cores from the ...
Goldschmidt2021 abstracts
Environmental Toxicology and Chemistry
The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data prod... more The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. Th...
Environmental science & technology, Jan 17, 2018
Historical reconstruction of mercury (Hg) accumulation in natural archives, especially lake sedim... more Historical reconstruction of mercury (Hg) accumulation in natural archives, especially lake sediments, has been essential to understanding human perturbation of the global Hg cycle. Here we present a high-resolution chronology of Hg accumulation between 1727 and 1996 in a varved sediment core from the Pettaquamscutt River Estuary (PRE), Rhode Island. Mercury accumulation is examined relative to (1) historic deposition of polycyclic aromatic hydrocarbons (PAHs) and lead (Pb) and its isotopes (Pb/Pb) in the same core, and (2) other reconstructions of Hg deposition in urban and remote settings. Mercury deposition in PRE parallels the temporal patterns of PAHs, and both track industrialization and regional coal use between 1850 and 1950 as well as rising petroleum use after 1950. There is little indication of increased Hg deposition from late 19th-century silver and gold mining in the western U.S. A broad maximum of Hg deposition during 1930-1980, and not found in remote sites, is consi...
Deep Sea Research Part I: Oceanographic Research Papers, 2016
Low-molecular weight thiols, including cysteine and glutathione, are biomolecules involved in a v... more Low-molecular weight thiols, including cysteine and glutathione, are biomolecules involved in a variety of metabolic pathways and act as important antioxidant and metal buffering agents. In this last capacity, they represent a potential mechanism for modulating the bioavailability and biogeochemistry of many trace elements in the ocean, particularly for chalcophilic elements (e.g., Cu, Zn, Cd, Ag and Hg). For this reason, and in the context of the international GEOTRACES program that seeks to understand the biogeochemistry of trace elements in the ocean, we measured the concentration of individual dissolved low-molecular weight thiols during the U.S. GEOTRACES North Atlantic Zonal Transect (USGNAZT). Only two thiols were identified, cysteine and glutathione, in contrast to results from the northeast subarctic Pacific Ocean, where the dipeptides glycine-cysteine and arginine-cysteine were also present and -glutamylcysteine was dominant. Concentrations of cysteine and glutathione in the North Atlantic Ocean were lower than in the Pacific and ranged from below detection (~0.01 nM) to 0.61 nM of cysteine and up to 1.0 nM of glutathione, with cysteine generally more abundant than glutathione. Vertical profiles of cysteine and glutathione were broadly consistent with their biological production, being more abundant in surface water and usually below detection at
Environmental science & technology, Jan 18, 2016
Metals in sediment can be complexed by minerals, partition between solid and aqueous phases, and ... more Metals in sediment can be complexed by minerals, partition between solid and aqueous phases, and cause toxicity at high concentrations. We studied how the oxidation of surface sediment that occurs during aging alters the partitioning and toxicity of Ni. Two sediments (Burntwood and Raisin) were amended with Ni, equilibrated, incubated in a flow-through flume, and examined for sediment physicochemistry and toxicity to Hyalella azteca (7 day growth). Through time, the sediment surface (5 mm) was oxidized, acid-volatile sulfide concentrations declined in Raisin sediment, and amorphous Fe oxides increased. Porewater Ni concentrations declined through time but total Ni concentrations in sediment were unchanged, suggesting changes in Ni partitioning through time. Both sediments elicited a toxic dose-response by H. azteca early in the aging process; but only Burntwood, for which Ni was primarily partitioned to Fe oxide minerals, exhibited a consistent dose-response during aging. Low total ...
ABSTRACT Abstract (2 leaves) bound with copy. Thesis (Ph. D.)--University of Connecticut, 2005. I... more ABSTRACT Abstract (2 leaves) bound with copy. Thesis (Ph. D.)--University of Connecticut, 2005. Includes bibliographical references. Adviser: William F.
Environmental Science Technology, 2005
Development of the early life stages of fishes can be affected adversely by methylmercury (MeHg) ... more Development of the early life stages of fishes can be affected adversely by methylmercury (MeHg) transferred from the maternal parent to the developing egg. We examined maternal transfer of MeHg to eggs of fathead minnows Pimephales promelas and evaluated the role of maternal MeHg burden versus that in the maternal diet during oogenesis on egg concentrations. Juvenile fish were fed one of four diets until sexual maturity (phase 1): A control diet (0.06 µg of Hg g-1 dry weight) and three that were contaminated with MeHg at 0.88 (low), 4.11 (medium), and 8.46 µg of Hg g-1 (high). At sexual maturity, female fish were paired with a male, again fed one of the four diets, and allowed to reproduce (phase 2). To assess the significance of female dietary exposure during oogenesis on MeHg in eggs, some fish were fed diets during phase 2 that differed from those during phase 1. Mean concentrations and burdens of MeHg in eggs from fish fed the same diet throughout the experiment varied with MeHg content of the maternal diet and were related positively to levels in the carcass of the maternal fish. However, MeHg in eggs was not proportional to that in carcasses among dietary treatments; MeHg in eggs from adults fed the control, low, medium, and high MeHg diets averaged 14%, 25%, 32%, and 35% of that in adults. For fish fed the control diet as juveniles and MeHg-contaminated diets after reaching sexual maturity, MeHg in eggs increased rapidly with duration of maternal dietary exposure prior to spawning. Moreover, concentrations of MeHg in eggs from fish fed the same contaminated diet as both juveniles and sexually mature adults were not related to the duration of adult exposure, and they were not appreciably greater than those from fish fed contaminated diets only just prior to spawning. These results indicate that the diet of the maternal adult during oogenesis, and not adult body burden, is the principal source of MeHg in fish eggs. Accordingly, the exposure of embryonic wild fishes to MeHg depends on levels of the contaminant in prey of the adult during oogenesis, which can vary intra-and interannually.
Environ Sci Technol, 1999
We examined the influence of maternal mercury and selected lacustrine variables on the mercury co... more We examined the influence of maternal mercury and selected lacustrine variables on the mercury content of eggs from yellow perch (Perca flavescens). Total mercury, methylmercury, and inorganic mercury were determined in eggs and carcasses (less eggs) from three seepage lakes with a pH range of 6.1-7.0 and a fourth lake in which pH was experimentally increased from 5.5 to 6.8 by addition of alkaline groundwater. The concentration of total mercury in eggs was strongly correlated with that in the maternal carcass. Concentrations and burdens of mercury in eggs and carcasses were inversely correlated with lake water pH, acid-neutralizing capacity, calcium, and dissolved organic carbon. In eggs containing more than 30 ng/g dry weight (4.5 ng/g wet weight) of total mercury, methylmercury averaged 91% of total mercury and ranged from 85% to 96%. Mean burdens of total mercury in individual eggs varied greatly among lakes (range, 2.3-63 pg), and the egg mass averaged 1.9% of the whole-body burden. We conclude that exposure of the developing yellow perch embryo to methylmercury is strongly affected by maternal bioaccumulation, which can vary substantially among and within lakes; however, the toxicological significance of the observed exposure of embryos to methylmercury is unclear.
Environmental Science and Technology, Sep 1, 2003
A new method for the determination of the concentration and conditional stability constant of dis... more A new method for the determination of the concentration and conditional stability constant of dissolved organic matter that binds mercury (Hg) has been developed using an in vitro assay of reducible Hg. The technique is a wet chemical analogue to electrochemical approaches now in use for ligand studies of many other trace transition metals in natural waters. Ligand characteristics are obtained from additions of ionic Hg to buffered lake, river water, and seawater and determination of the wet chemically reducible fraction following equilibration of the spike. This approach is robust, as demonstrated by (i) analysis using three reducing agents of varying strengths, (ii) replicate analyses, (iii) comparison to well-characterized complexing species (chloride and EDTA) using a competitive ion-exchange resin, and (iv) kinetic studies. Results indicate that Hg-complexing equivalents are present in the dissolved phase (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.2 microm) ranging from &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;1 to &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;60 nN concentrations and with log conditional stability constants (log K&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;) in the range of 21-24. Only one ligand class was found in the natural waters analyzed. There was indirect evidence for a class of organic ligands that formed reducible complexes with Hg in freshwater. Such ligand characteristics indicate that the vast majority of ionic inorganic Hg dissolved in freshwater and coastal saltwaters is associated with organic complexes. Concentrations, affinities, and kinetics implicate multidentate chelation sites as the principal complexing moieties for Hg and discourage the use of humic carboxylic acids as a proxy for the ligands/functional groups.
Environmental Science & Technology, 2016
Environmental Toxicology and Chemistry, 2015
Periphyton uptake of bioaccumulative methylmercury (MeHg) may be an important entryway into the f... more Periphyton uptake of bioaccumulative methylmercury (MeHg) may be an important entryway into the food web of many stream ecosystems where periphyton can be dominant primary producers. The net production of MeHg in stream sediment, its bioaccumulation in periphyton, and potential toxicity of divalent Hg (Hg(II)) and MeHg in sediment to periphyton were investigated with a 67-day in situ incubation experiment using chemical exposure substrates containing either a fine-grained, organic-rich or sandy, low-organic sediment, each amended with varying concentrations of mercuric chloride. MeHg was produced in sediment and concentrations increased with greater amounts of added Hg(II); however, the net production of MeHg was inhibited in the highest Hg(II) treatments of both sediments. The range of total Hg concentrations that inhibited MeHg production were between about 80,000 and 350,000 ng Hg per gram of organic matter for both sediments. Periphyton colonizing substrates accumulated MeHg in proportion to the concentration in sediment, but periphyton exposed to the sandy sediment accumulated about 20-fold more than those exposed to the organic-rich sediment relative to sediment MeHg concentrations. Toxicity of either Hg(II) or MeHg to periphyton was not observed with either periphyton organic content, net primary production, or respiration as endpoints. These results suggest that in situ production and bioaccumulation of MeHg in stream ecosystems can vary as a function of sediment characteristics and Hg(II) loadings to the sediment. This article is protected by copyright. All rights reserved.
Environmental Pollution, 2015
Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended so... more Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended solids (TSS), and other complexing ligands; however, no studies have examined the relative importance of Ni exposure through different compartments (water, sediment, food). Hyalella azteca and Lymnaea stagnalis were exposed to Ni-amended water, sediment, and food, either separately or in combination. Both organisms experienced survival and growth effects in several Ni compartment tests. The DOC amendments attenuated L. stagnalis Ni effects (survival, growth, and (62)Ni bioaccumulation), and presence of TSS exposures demonstrated both protective and synergistic effects on H. azteca and L. stagnalis. (62)Ni trophic transfer from food to H. azteca and L. stagnalis was negligible; however, bioaccumulating (62)Ni was attributed to (62)Ni-water ((62)Ni flux from food), (62)Ni-TSS, and (62)Ni-food. Overall, H. azteca and L. stagnalis Ni compartment toxicity increased in the following order: Ni-water &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; Ni-sediment &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; Ni-all (water, sediment, food) &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; Ni-food.
Environmental Science & Technology, 2015
To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico... more To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico (GOM) fish, we quantified fluxes of total Hg and MeHg from 11 rivers in the southeastern United States, including the 10 largest rivers discharging to the GOM. Filtered water and suspended particles were collected across estuarine salinity gradients in Spring and Fall 2012 to estimate fluxes from rivers to estuaries and from estuaries to coastal waters. Fluxes of total Hg and MeHg from rivers to estuaries varied as much as 100-fold among rivers. The Mississippi River accounted for 59% of the total Hg flux and 49% of the fluvial MeHg flux into GOM estuaries. While some estuaries were sources of Hg, the combined estimated fluxes of total Hg (5200 mol y(-1)) and MeHg (120 mol y(-1)) from the estuaries to the GOM were less than those from rivers to estuaries, suggesting an overall estuarine sink. Fluxes of total Hg from the estuaries to coastal waters of the northern GOM are approximately an order of magnitude less than atmospheric deposition rates. However, fluxes from rivers are significant sources of MeHg to estuaries and coastal regions of the northern GOM.
Environmental toxicology and chemistry / SETAC, Jan 27, 2015
Sediments in navigation-dominated waterways are frequently contaminated with a variety of particl... more Sediments in navigation-dominated waterways are frequently contaminated with a variety of particle-associated pollutants and are subject to frequent short-term resuspension events. There is little information documenting whether resuspension of metal-contaminated sediments has adverse ecological effects on resident aquatic organisms. Using a novel laboratory approach, we examined the mobilization of Zn, Cu, Cd, Pb, Ni and Cr during resuspension of a freshwater and two coastal marine sediments and whether resuspension and redeposition resulted in toxicity to model organisms. Sediment flux exposure chambers (SeFEC) were used to resuspend metal-contaminated sediments from one site in Lake DePue, Illinois, and two sites in Portsmouth Naval Shipyard, Maine. Short-term (4 h) resuspension of sediment at environmentally relevant suspended particulate matter concentrations (< 1 g/L) resulted in metal mobilization to water that was sediment and metal specific. Overall, the net release of m...
Our research in the U.S. Arctic is focused on (a) atmospheric Hg deposition and contamination of ... more Our research in the U.S. Arctic is focused on (a) atmospheric Hg deposition and contamination of lakes and watersheds, (b) in-lake cycling of Hg, especially methylHg, and (c) the behavior and fate of elemental Hg, whose production and mobilization via water-air exchange are quite significant. These studies are being conducted in the lacustrine and tundra wetland environs near the Arctic LTER Site at the Toolik Field Station (68\deg 38' N, 149\deg 38' W). Atmospheric Hg deposition over the last several centuries has been established with dated sediment archives from five carefully selected (i.e., headwater; small watershed) remote arctic lakes. Mercury budgets for the study lakes have been constructed from atmospheric, water column, watershed, and sedimentary investigations. Results indicate that (1) impact from anthropogenic Hg in the Arctic is of similar magnitude to that at temperate latitudes; (2) whole-lake Hg sedimentation determined using 55 210Pb-dated cores from the ...